Manchester United defender Lisandro Martínez will undergo surgery on his right foot for an injured metatarsal, manager Erik ten Hag said on Monday.
Martinez has already been ruled out for an "extended period" after a recurrence of the injury that saw him miss the end of last season.
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The Argentina international will have a second operation on his foot, having initially had surgery in April to repair his fractured metatarsal.
"That's really sad, disappointing news," Ten Hag said ahead of United's Champions League game against Galatasaray on Tuesday. "He has to go through the same process and I'm really sorry for him.
"The squad will miss him. As you know, we have more injuries, so we always have to deal with it as a squad ... He has to be strong. He will fight back, I'm sure. He is a character."
Ten Hag is also without defenders Tyrell Malacia, Sergio Reguilón, Luke Shaw and Aaron Wan-Bissaka against the Turkish champions at Old Trafford.